Wireless communications are rapidly augmenting conventional telephone communications. In conventional telephone communications, emergency 911 service has been in existence for a number of years and has evolved and been upgraded over time. Currently, from most wired telephone systems, an "Enhanced 911" service is available. In Enhanced 911 service, the emergency center receiving the call automatically learns the phone number, location and identity of the calling party. Such information is necessary for rapidly dispatching the required help to the correct location, and for call-back to the party that reported the emergency, if required. Indeed, Enhanced 911 is so common, that there is an expectation and assumption by the public, that such service is available in the wireless world. However, at the current time, Enhanced 911 service does not exist for cellular telephony which is the most mature wireless communication system in the United States. At the current time, an emergency center that receives a call dialed from a cellular telephone, has no idea where the party is calling from and does not know the phone number or identity of the phone subscriber. Furthermore, there exists no infrastructure or standard for providing Enhanced 911 service in cellular and other wireless communications systems.
Determining the position of the calling terminal making a wireless call is a key requirement for providing Enhanced 911. A number of alternatives for determining position of a caller are based upon the calling terminal estimating its position with the support of auxiliary equipment and/or the use of broadcast RF beacons. Available options for position location at the calling terminal are as follows:
1. Broadcast Navigation RF Beacons: GPS and Loran are two examples. PA0 2. Commercial Broadcasts as Navigation Beacon Surrogates: such as using the broadcasts of AM, FM or TV for determining position. (See, for example, U.S. Ser. No. 08/203,257, and PCT Application No. PCT/US93/12179, incorporated herein by reference) PA0 3. Base Station to Mobile/Portable Terminal Broadcasts as Navigation Beacon Surrogates: such as using the broadcasts from multiple cellular base stations. PA0 4. Dead Reckoning and other forms of Inertial Navigation: such as using the speedometer output of a vehicle in combination with a gyroscope to detect turns.
Because of the variety of wireless environments and services, none of these options provides a universal solution for determining position of the calling terminal. For example, in the cellular world, there are two distinctly different environments for mobiles and portables. Mobile terminals are defined as those that are installed in and operate from vehicles. Thus the locations for the mobile environment are restricted to places that a vehicle may go. Portable terminals are defined as hand-held devices and so portables will be used anywhere that a person may go with or without a vehicle. Thus mobiles and portables are different insofar as the places that they are required to operate in. Mobiles must work primarily on streets and highways where there is often a clear view of the GPS constellation; and when there is not, such as in the "urban canyon," GPS position fixing is still possible, albeit on an interrupted basis. Portables however, will be used inside buildings, shopping malls, and parking garages where cellular communications signals penetrate, but GPS signals do not. Furthermore, mobiles (unlike portables) are not particularly constrained with respect to size and power; thus, the vehicle that hosts the mobile can support the power required for continuous position fixing; they can support the equipment needed for dead reckoning; and finally, they provide a platform on which to attach antennas (i.e., GPS) that must be mounted in a fixed orientation.